In an evolution process of a Long Term Evolution (LTE for short) system, to increase a spectral bandwidth of the system, a carrier aggregation technology is proposed in the third generation partnership project (3GPP for short). In the carrier aggregation technology, multiple consecutive or inconsecutive carriers are aggregated to form a wider spectrum. When a base station configures multiple carriers, the base station may send data to user equipment (UE for short) simultaneously by using the multiple configured carriers. When the base station sends data to the UE by using a scheduled carrier (a carrier used by the base station to transmit data) in the configured carriers (the carriers configured by the base station), the base station needs to send downlink control information (DCI for short) to the UE by using each scheduled carrier, to indicate to the UE information such as a physical resource block occupied by the base station on the scheduled carrier, and modulation and coding schemes used by the base station, so that the UE receives data according to the received DCI.
In the prior art, in order that UE can learn scheduling statuses of all configured carriers of a base station, the base station may add a downlink assignment indication (DAI for short) 2 field to the DCI sent to the UE, to indicate scheduling statuses of configured carrier different from the current scheduled carrier (the carrier used to transmit the DCI). A quantity of bits of the DAI2 field is determined according to a quantity of the configured carriers of the base station, and the quantity of bits is equal to the quantity of the configured carriers of the base station minus 1.
At least the following problem exists in the prior art. Because in the prior art, the DAI2 field needs to indicate the scheduling statuses of the configured carriers different from the current scheduled carrier, the quantity of bits of the DAI2 field is equal to the quantity of the configured carriers of the base station minus 1. In this way, when the base station configures a relatively large quantity of carriers, the DAI2 field includes more bits. Consequently, the DCI is relatively long, and signaling overheads are relatively large.